More particularly, the invention is situated in the field of communications systems of the multichannel type.
Acoustic echo exists mainly in certain types of communication where the terminal of a distant user comprises one or more loudspeakers substituted for the earpiece and one or more microphones. It is a question for example of audio conference equipment or handsets functioning in “hands free” mode such as mobile telephones. Without special precautions, the sound emitted by the loudspeaker undergoes multiple reflections (against walls, the ceiling, etc) constituting a number of different echoes that are picked up by the microphone in the same way as the useful speech. The assembly consisting of the loudspeaker, the microphone and their physical environment thus constitutes an echo generating system.
In the case of a multichannel device, an echo cancelling system comprises N signal reception channels comprising a loudspeaker Hpi (i=1, 2, . . . ,N) and M sound pickup channels, each sound channel comprising a set of microphones MCj (j=1, 2, . . . ,M). This system thus comprises N*M acoustic channels and N*M echo cancellation devices II (i,j).
In the context of the use of a plurality of audio conference equipments or handsets functioning in “hands free” mode in the same premises, cross echo phenomena arise.
Thus, if several persons situated in the same premises close to one another are in “hands free” telephone communication with distant interlocutors, the signals reproduced by the loudspeaker of each telephone equipment are picked up by the microphone of each telephone equipment present in the premises and thus retransmitted to each distant caller. At the “hands free” telephone equipment, no echo cancellation is made on the signals reproduced by the loudspeakers of the other telephone handsets close to the telephone equipment. This appreciably interferes with communication and makes the use of several “hands free” telephone equipments impossible in the same premises.
Thus the echo correction mechanisms of the prior art do not correctly correct echoes when many communication devices close to one another are functioning simultaneously.